The present invention relates to apparatus for continuously making a continuous helically wound tubular structure of interlocked metal strip.
Applicants' Assignee has developed and marketed for various applications, and especially for undersea petroleum exploitation, flexible tubular pipes and conduits having high mechanical strength characteristics, particularly, resistance to traction, and resistance to both internal and external pressures, particularly, the pressure of hydrocarbons, flowing through the pipes.
Such pipes usually have at least one layer in the form of a tubular structure of interlocked strip wound in a helix, the winding having a basically S- or Z-shaped cross-section allowing mutual interlocking.
Such a tubular structure is thus used in the "rough bore" type of pipe to form the internal carcass of the pipe which constitutes a reinforcement or casing.
In this type of pipe, for certain applications, there may also be used at least one other tubular layer of helical interlocked strip forming a layer designated to reinforce the resistance of the pipe and to internal and external pressures. The helical interlocked strip structure windings are normally separated from the interior casing by a sheath of thermoplastic material. The pipe is generally completed by one or more layers of reinforcing wires or strips and has an exterior thermoplastic sheath for sealing and anti-corrosion protection.
In another type of pipe, called "smooth bore", in which the inside layer is a thermoplastic layer, one or more reinforcing layers each of an interlocked helical wound structure are used.
Interlocked helical wound tubular structures also have applications in other types of flexible or rigid pipes.
There is already known, apparatus to make a long continuous length of an interlocked helical wound tubular structure, this apparatus having a supply of winding strip previously shaped so as to present a basically S- or Z-shaped interlocking section, a fixed winding station having a plurality of pressure fingers to interlock the shaped strip, a mechanism for removing the formed tubular structure, and a reel for its storage. Of course, to form the helical wound tubular structure it is necessary to cause the tubular structure to rotate about its longitudinal axis. To accomplish this, it is necessary to cause the receiving reel for the formed tubular structure to rotate around the longitudinal axis of the formed structure as well as around a transverse axis. The reel must thus be mounted in a frame or casing which is able to turn around the longitudinal axis of the formed tubular structure, means also being provided to make the reel turn in the frame around a transverse axis. In addition, it is necessary to make the withdrawal mechanism turn around the same longitudinal axis of the formed tubular structure, the withdrawal mechanism then being mounted in a turning frame which must be driven in synchronization with the casing or frame containing the receiving reel.
When it is recognized that in order to produce tubular helical wound structures of great length the receiving reels must be several meters in diameter, and the complexity of the device as a result of the need to cause significant masses to turn in synchronization becomes apparent. This complexity is further increased when the tubular structure must be formed around a core, such as a sheath of thermoplastic material or a structure with one or more previously formed layers, because in this case, the core must also rotate around its longitudinal axis, and for this purpose, the reel from which the core unwinds, particularly when the core is flexible, must also be mounted on a support driven in rotation around the longitudinal axis, the rotational movement of this reel naturally being synchronized with the rotational movement of the frame of the receiving reel and the frame of the withdrawal mechanism.
In addition, there is known from British Pat. No. 110,576 apparatus including a circular plate turning around a horizontal axis coincidant with the longitudinal axis of the tubular structure to be formed. This apparatus includes, on the same side of the plate, a support for a supply reel of flat strip, an assembly of driven shaping rollers to drive the strip and to give it a basically S- or Z-shaped cross-section, guiding means for the strip between the supply reel and the assembly of shaping rollers, a tubular mandrel mounted coaxially on the plate near the center of the plate, and an extraction mechanism for longitudinal removal of the tubular structure formed, placed downstream of the turning plate to withdraw the structure formed toward a receiving reel.
In addition to the fact that it was not possible with the prior apparatus to form an interlocked wound strip tubular structures around a core, significant disadvantage of the prior apparatus arose from the impossibility of controlling the interlocking and the tightening of the windings of the shaped strip, at the time of its winding on the mandrel. For each strip, a driven roller only is provided near the mandrel. Such an arrangement does not ensure good tightening of the windings of the strip and, in addition, because of the driving connections between the central roller and the other shaping rollers, it is not possible to easily change the position of the central roller especially when changing from one diameter of manufactured conduit to another.